I tease non-Texans that Texan English is actually superior to normal American English because it supports second-person plural via "Y'all" exactly as mentioned in this article... "you guys" is, to some ears, sexist, and "youse guys" (a New York-ism) is a little too old-school Italian. English lost its second person plural when we switched from Thou (second person singular formal + Thee=second person singular informal…
Thou and Thee are nominative and objective cases. Same for You and Ye. The formality/informality distinction is between You/Ye and Thou/Thee. Plural 2nd person used to formally address a single individual came to English from French, thanks to the Norman Conquest. French, I think, inherited it from Latin, and the custom of addressing the emperor with the plural. After a while it became rude to address people with the…
Use "thou" where one would use "I" if discussing onesself. Use "thee" where one would use "me".